This invention relates generally to the field of refrigeration unit compressors, and more particularly to a refrigeration unit compressor which becomes flooded when not operated for a period of time.
It is commonly known that, in a refrigeration system, starting any compressor with its crankcase filled with liquid refrigerant causes premature wear or failure of some compressor components, such as the suction and discharge valves, the thrust washer, the piston/rod assembly, the connecting rod bearing, and the main bearing. The problem arises because the oil that lubricates the compressor parts becomes saturated with the refrigerant in the system during extended periods when the system is not operating. A way of preventing damage caused by a flooded start is needed.
Briefly stated, when a flooded compressor in a refrigeration unit begins to run, refrigerant that has been absorbed into the oil is suddenly released, causing the crankcase to be filled with a sudsy mixture of refrigerant and oil. This mixture is then drawn into the suction manifold, cylinders, and compressor heads, in addition to being pumped out into the refrigeration system. When a flooded compressor startup condition in a mobile refrigeration unit is sensed, the compressor is shut down for a specified period of time to allow the oil in the system and on the compressor heads to drain back into the compressor oil sump before running the compressor again. The flooded compressor condition is determined by checking whether a suction superheat, a discharge superheat, and a suction pressure are all within specified operating parameters for a specified period of time after the compressor is started.
According to an embodiment of the invention, a method for detecting a flooded compressor startup condition in a mobile refrigeration unit includes the steps of (a) determining whether the compressor is running, and if so, starting a timer; (b) determining, after the timer is started, whether a discharge superheat of the unit is less than a first predetermined temperature, and if so, determining whether a suction superheat of the unit is less than a second predetermined temperature, and if so, determining whether a suction pressure of the unit exceeds a predetermined pressure, and if so, determining whether the timer exceeds a first predetermined period of time; (c) determining, after step (b) is completed and after the timer exceeds the first predetermined time, whether the suction superheat is less than the second predetermined temperature, and if so, determining whether the discharge superheat is less than the first predetermined temperature, and if so, determining whether the timer exceeds a second predetermined period of time; and (d) stopping, after step (c) is completed and after the timer exceeds the second predetermined period of time, the compressor.
According to an embodiment of the invention, a method for detecting a flooded compressor startup condition in a mobile refrigeration unit includes determining whether a suction superheat of the unit, a discharge superheat of the unit, and a suction pressure of the unit are all within specified operating parameters for a first specified period of time after the compressor is started, and if so, stopping the compressor for at least a second specified period of time.
According to an embodiment of the invention, an apparatus for detecting a flooded compressor startup condition in a mobile refrigeration unit includes means for determining whether the compressor is running, and if so, starting a timer; means for determining, after the timer is started, whether a discharge superheat of the unit is less than a first predetermined temperature, and if so, determining whether a suction superheat of the unit is less than a second predetermined temperature, and if so, determining whether a suction pressure of the unit exceeds a predetermined pressure, and if so, determining whether the timer exceeds a first predetermined period of time; means for determining whether the suction superheat is less than the second predetermined temperature after the timer exceeds the first predetermined time, and if so, determining whether the discharge superheat is less than the first predetermined temperature, and if so, determining whether the timer exceeds a second predetermined period of time; and means for stopping the compressor after the timer exceeds the second predetermined period of time.
According to an embodiment of the invention, an apparatus for detecting a flooded compressor startup condition in a mobile refrigeration unit includes means for determining whether a suction superheat of the unit, a discharge superheat of the unit, and a suction pressure of the unit are all within specified operating parameters for a first specified period of time after the compressor is started, and if so, means for stopping the compressor for at least a second specified period of time.